Photochemical skeletal editing: one-step transformation of diaryl dithiophenes into regiodefined helicenes

Abstract

Skeletal editing is reshaping synthetic design to allow the direct, atom-level manipulation of molecular frameworks. While single-atom insertion or deletion has been achieved in simple aromatic systems, strategies for editing S-heterocycles within complex, functional molecules remain underdeveloped due to the inertness of C–S bonds and the lack of mild, direct methods to reconstruct the entire aromatic skeleton. We report a photochemical skeletal editing approach that directly converts readily available diaryl dithiophenes into regiodefined π-extended helicenes, bypassing the multistep sequences and regioselectivity limitations of classical syntheses. This transformation consists of the formation of two benzene rings and a ring opening of thiophene through cascade-initiated steps under light. The process involves regioselective photocyclization, followed by C–S bond cleavage, a second annulation and desulfurization, all occurring in a one-pot synthetic operation. The reaction proceeds under mild conditions, displays broad substrate scope, and enables the efficient regioselective synthesis of diverse benzo-fused helicenes. The resulting π-extended helicenes exhibit good photophysical and chiroptical properties. Their performance in terms of circularly polarized luminescence (CPL) shows attractive luminescence dissymmetry factors (|g_lum|) reaching magnitudes of the order of 10⁻³.